Solution-Processed Fabrication of Light-Emitting Diodes Using CsPbBr₃ Perovskite Nanocrystals

The sonochemical synthesis of CsPbBr3 perovskite nanocrystals (PNCs) is an attractive method for the large-scale synthesis and low-cost production of PNC at low temperature; however, there are no reports on their application to robust film formation and light-emitting diodes (LEDs). In this study, ultrasonic-assisted synthesis of CsPbBr3 PNCs was reported by using precursors (Cs2CO3 and PbBr2) and ligands (oleic acid (OA) and oleylamine (OAm)). The ratios of the Cs2CO3:PbBr2 and OA:OAm were controlled to enhance the photoluminescence (PL) of the PNCs. Furthermore, by adjusting these ratios, we observed the transition of the PNCs from the rhombohedral Cs4PbBr6 phase to the monoclinic CsPbBr3 phase. In addition, by optimizing the Cs2CO3:PbBr2 and OA:OAm ratios, we obtained CsPbBr3 PNCs with the highest PL intensity in both solutions and films. Finally, a high-quality PNC-coated film was obtained by purifying the CsPbBr3 PNCs with methyl acetate (MeOAc) and used for LED device fabrication whereby the MeOAc provided solvent orthogonality during the electron transport layer (ETL) coating. Thus, a solution-processed PNC-LED comprising dual ETLs of 2,2′,2″-(1,3,5-benzinetriyl)tris(1-phenyl-1H-benzimidazole) (TPBi) and ZnO nanoparticles was fabricated. The dual ETL PNC-LED device showed enhanced LED device performance (lower turn-on voltage and high brightness) compared to the single ETL PNC-LED device. Furthermore, improved charge balance was achieved by using a Mg-doped ZnO ETL.